// note, that we don't have `runBlocking` to the right of `main` in this example
fun main(args: Array<String>) {
val time = measureTimeMillis {
// we can initiate async actions outside of a coroutine
val one = asyncSomethingUsefulOne()
val two = asyncSomethingUsefulTwo()
// but waiting for a result must involve either suspending or blocking.
// here we use `runBlocking { ... }` to block the main thread while waiting for the result
runBlocking {
println("The answer is ${one.await() + two.await()}")
}
}
println("Completed in $time ms")
}

'Unconfined': I'm working in thread main
'coroutineContext': I'm working in thread main
'Unconfined': After delay in thread kotlinx.coroutines.DefaultExecutor
'coroutineContext': After delay in thread main

子协程

fun main(args: Array<String>) = runBlocking<Unit> {
// start a coroutine to process some kind of incoming request
val request = launch(CommonPool) {
// it spawns two other jobs, one with its separate context
val job1 = launch(CommonPool) {
println("job1: I have my own context and execute independently!")
delay(1000)
println("job1: I am not affected by cancellation of the request")
}
// and the other inherits the parent context
val job2 = launch(coroutineContext) {
println("job2: I am a child of the request coroutine")
delay(1000)
println("job2: I will not execute this line if my parent request is cancelled")
}
// request completes when both its sub-jobs complete:
job1.join()
job2.join()
}
delay(500)
request.cancel() // cancel processing of the request
delay(1000) // delay a second to see what happens
println("main: Who has survived request cancellation?")
}

代码执行结果如下

job1: I have my own context and execute independently!
job2: I am a child of the request coroutine
job1: I am not affected by cancellation of the request
main: Who has survived request cancellation?

结合上下文

协程上下文可以通过+操作符结合在一起，右边的上下文会代替左边的上下文。举个例子，当替换掉调度器的时候，父协程的Job可以被继承。

fun main(args: Array<String>) = runBlocking<Unit> {
// start a coroutine to process some kind of incoming request
val request = launch(coroutineContext) { // use the context of `runBlocking`
// spawns CPU-intensive child job in CommonPool !!!
val job = launch(coroutineContext + CommonPool) {
println("job: I am a child of the request coroutine, but with a different dispatcher")
delay(1000)
println("job: I will not execute this line if my parent request is cancelled")
}
job.join() // request completes when its sub-job completes
}
delay(500)
request.cancel() // cancel processing of the request
delay(1000) // delay a second to see what happens
println("main: Who has survived request cancellation?")
}

执行结果如下

job: I am a child of the request coroutine, but with a different dispatcher
main: Who has survived request cancellation?

Actors

There is an actor coroutine builder that conveniently combines actor's mailbox channel into its scope to receive messages from and combines the send channel into the resulting job object, so that a single reference to the actor can be carried around as its handle.